On Tuesday, Markle and Prince Harry attended a garden party at Buckingham Palace for Prince Charles’s 70th birthday, marking their official debut as the Duke and Duchess of Sussex. Markle wore a $643 pink and taupe silk Goat dress with sheer long sleeves and a Philip Treacy hat, and she carried a Wilbur and Gussie clutch. But the detail that truly earned her royal status was a pair of sheer tights.

It was the first time she wore tights to a royal function, having raised eyebrows in the past for going bare-legged, for example in April when attending the Invictus Games Sydney celebration in London wearing a $510, green floral Self-Portrait dress and in December during her engagement announcement, when she wore a $750 Line the Label white coat over a green dress by P.A.R.O.S.H.

Granted, some of these women grew up during the era of nylons, which were invented in 1959 and considered essential for dignified events. However, unlike most millennials, Middleton wears them regularly, and the fact that Markle — a former fashion blogger — wore them to kick off her royal career suggests that hosiery is nonnegotiable.

Kate Middleton, like other female members of the royal family, must wear pantyhose in public. (Photo: Getty Images)

“Generally speaking, the queen is pretty progressive, but she does require all women in the family to wear pantyhοse if they choose to wear dresses or skirts,” Kelly Lynch, royal expert and managing editor of Dailybreak, tells Yahoo Lifestyle. “The simple reason is, Her Majesty considers it ladylike, proper, and appropriate, and it’s the one rule she won’t budge on, regardless of temperature.”

Middleton usually opts for flesh-toned hosiery with her rumored brand being $7 John Lewis Barely There nonslip tights with gel cushions. In fact, the Duchess of Cambridge has become so synonymous with nylons that in 2012, British supermarket chain Asda noted that its hosiery sales had risen by 500 percent thanks to the “Kate effect,” a trend that causes an influx of business for Middleton’s favored brands.

Pantyhοse aren’t the only fashion rule imposed by the palace — boys under the age of 8 must wear shorts, even in cold weather (however, Prince George was allowed to wear black pants for the royal wedding), per aristocratic tradition. And little girls like Princess Charlotte are reportedly banned from wearing dresses until the age of 1, with exceptions made for official family photos.

“The queen also asks that royal women sew light weights into their skirts to prevent wind-blown accidents, which has happened to Kate Middleton on several occasions,” notes Lynch.

Markle’s style is unpredictable — she’s sported messy buns, all-black attire, and a cross-body bag, all three of which break royal protocol. But that could be good, says Lynch: “If Meghan doesn’t like pantyhοse, she might give us the royal pantsuit.”